Distinguishing between bacterial and viral Lower Respiratory Tract Infections (LRTI) can be challenging. ImmunoXpert™ is a novel immunoassay that distinguishes between bacterialand viral infections based on the patient’s immune response. The assay combines both viral- and bacterial-induced host-proteins (TRAIL, IP-10 and CRP), and computes a bacterial likelihood score. Here we compare the assay performance with standard laboratory and clinical parameters that are routinely used in clinical practice to facilitate diagnosis of LRTIs in febrile children and adults.We studied 125 patients (55 adults and 70 children) with bacterial or viral LRTIs, as determined by unanimous agreement of three independent physicians following comprehensive clinical and laboratory investigation (physical examination, medical history, complete blood count, chemistry panel and a multiplex PCR panel applied on nasal swabs [Seeplex RV15 and PB6]). A bacterial likelihood score was computed for each patient using the serum levels of the three host-proteins (Oved et al. 2015), and compared to the reference standard diagnosis.
expert panel diagnosis yielded 89 bacterial and 36 viral diagnoses. The assay had a sensitivity of 0.92±0.06 and specificity of 0.91±0.09 for differentiating between bacterial (or mixed bacterial and viral co-infection) and viral infections after excluding 17 patients with an equivocal immune response. It outperformed routinely-used clinical parameters (and their combination) when applying routinely used cutoffs including white blood cell count (WBC, sensitivity 0.34±0.09, specificity 0.78±0.14; 15,000/µl cutoff;), absolute neutrophil count (ANC, sensitivity 0.43±0.1, specificity 0.81±0.14; 10,000/µl cutoff), maximal temperature (sensitivity 0.63±0.1; specificity 0.42±0.16; 40ºC/104ºF cutoff), CRP (sensitivity 0.9±0.06, specificity 0.61±0.15, 20 µg/ml cutoff; sensitivity 0.88±0.08, specificity 0.89±0.11, 50 µg/ml cutoff; and sensitivity 0.79±0.09, specificity 0.97±0.03, 80 µg/ml cutoff), and combination of ANC, WBC and CRP (sensitivity 0.86±0.07, specificity 0.89±0.11). Chest x-ray signs, typical of bacterial LRTI (consolidation or air bronchograms) attained sensitivity of 0.49±0.11 and specificity of 0.86±0.14. Other chest x-ray signs evaluated (diffuse interstitial or perihilar adenopathy) attained sensitivity of 0.69±0.1 and specificity of 0.39±0.19 (8 viral patients did not have chest x-ray).
ImmunoXpert™ has superior sensitivity and specificity, compared to standard laboratory and clinical parameters routinely used in clinical practice, for differentiation between bacterial from viral etiology for LRTI.
